Fluxes of biogenic components from sediment trap deployment in circumpolar waters of the Drake Passage

Circumpolar surface waters dominate the circulation of the Southern Ocean and sustain one of the ocean's largest standing stocks of biomass thereby producing a significant output of biogenic components, mainly diatoms, to the bottom sediments. Generally transit of biogenic matter from the sea surface to the sea floor affects nutrient regeneration fuels benthic life and transfers signals to the sediment record1–5. Reliable quantification of the relationship between biological production, fractionation of skeletal and tissue components and bottom sediment accumulation depends on direct vertical flux measurements from sediment trap deployments6–9, which have proved to be most scientifically productive10–13. We now present data on vertical mass fluxes from the Southern Ocean and evidence for strong biogeochemical fractionation between organic carbon-, nitrogen- and phosphorus-containing compounds, siliceous and calcareous skeletal remains, and refractory aluminosilicates

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Harmful Elements in Estuarine and Coastal Systems

Estuaries and coastal zones are dynamic transitional systems which provide many economic and ecological benefits to humans, but also are an ideal habitat for other organisms as well. These areas are becoming contaminated by various anthropogenic activities due to a quick economic growth and urbanization. This chapter explores the sources, chemical speciation, sediment accumulation and removal mechanisms of the harmful elements in estuarine and coastal seawaters. It also describes the effects of toxic elements on aquatic flora and fauna. Finally, the toxic element pollution of the Venice Lagoon, a transitional water body located in the northeastern part of Italy, is discussed as a case study, by presenting the procedures adopted to measure the extent of the pollution, the impacts on organisms and the restoration activities

Mechanism of human lymphotoxin and tumor necrosis factor induced destruction of cells in vitro: phospholipase activation and deacylation of specific-membrane phospholipids.

The role of phospholipase (PLase) activation and lipid metabolism in lymphotoxin (LT)- and tumor necrosis factor (TNF)-mediated destruction of murine L929 cells was examined. At the levels of LT and TNF employed, cell destruction began at 4-6 h and was 99% complete by 30 h. Cell membrane phospholipids (PL), labelled in situ at the C2 position with 14C arachidonic acid, were analyzed by two-dimensional thin-layer chromatography and quantitated over a 30 h time course after LT or TNF treatment. The ratio of radiolabel incorporation relative to the actual amount of each PL present was determined by inorganic phosphate analysis. Radiolabelled arachidonic acid, eicosanoids, and neutral lipids were released into the medium prior to the onset of cell death (4-6 h) and continued to accumulate linearly throughout the destructive reaction. There was a quantitative relationship between the appearance of radiolabelled metabolites in the media and the loss of radiolabelled cellular PL. Cellular phosphatidylethanolamine was the primary PL deacylated by PLase action, showing a 75% reduction in radiolabel. The PLase inhibitors--quinacrine, hydrocortisone, dexamethasone, and indomethacin--were potent inhibitors of LT- and TNF-mediated cell destruction, suggesting that selective deacylation of specific membrane PL by PLase activation is an important step in the events that lead to LT- and TNF-mediated cellular destruction in vitro

Carbon-cycle imbalances in the Sargasso Sea

The net exchange of carbon dioxide between the atmosphere and the ocean, and thus the nature of the oceanic carbon sink, is dominated by the seasonal dynamics of carbon cycling in the upper ocean. This cycle represents a balance between abiotic and biotic carbon transport into, and export out of, the ocean's upper layer. Here we report measurements of these processes made over five years in the Sargasso Sea off Bermuda, as part of the US Joint Global Ocean Flux Study (JGOFS). We find that the decrease in carbon stocks from the spring to the autumn in the upper 150 m of the ocean is three times larger than the measured sum of biotic and abiotic fluxes out of this layer. This discrepancy can be explained either by failure to account for horizontal advection of carbon or by inaccuracies in the fluxes of sinking particles as measured using sediment traps. Either the traps miss 80% of the sinking particles, or 70% of the carbon cycling is due to advection (or a combination of both processes is responsible). Sediment-trap measurements of the 234Th flux during this period suggest that most of the discrepancy may be due to inaccuracies in the trap methods, which would require a very general reassessment of existing ideas about particle export and remineralization of carbon in the oceans. If, on the other hand, advection is the main source of the discrepancy, the traditional one-dimensional (vertical) modelling of the oceanic carbon cycle cannot give a full account of carbon dynamics

Upward fluxes of particulate organic matter in the deep North Pacific

The flux of particulate matter through the oceanic water column is a primary component in elemental cycling and is generally perceived as being in one direction: downward1,2. The organic matter constituting these particles is produced through photosynthesis in surface waters and either sinks directly as phytoplankton and products3,4 or undergoes various trophic transformations through the water column. A large proportion of the particulate organic matter produced in surface waters is regenerated in the euphotic zone5-7. A fraction of this organic matter, however, leaves the surface waters and settles through the water column, generally decreasing in quantity and changing in quality with increasing distance from the surface8-11. Although the net transport of organic matter must be downward to fuel the lower portions of the water column, there is also an upward component to transport. Positively buoyant particles, including lipid-rich eggs, larvae and, possibly, carcasses of deep-sea animals are examples of particles which undergo upward transport12,13. A previous attempt to quantify the upward mass flux indicated rates of 1-4% of the downward mass flux14. Here we report the first evidence that there is a significant upward flux of particulate organic matter, up to 66.7% of the concurrently measured downward flux, at two stations in the deep North Pacific. Given this magnitude, the previously ignored upward flux of such organic matter must be considered in models of carbon and nitrogen cycling in the open ocean. © 1989 Nature Publishing Group